1. Field of the Invention
The invention relates to semiconductor resistive elements and was developed with particular attention to the possible use in high voltage applications.
2. Description of the Related Art
In general, in monolith semiconductor power apparatus, such as those made with VIPower technology developed by the Applicant, the need exists for having the substrate voltage partitioned within the control region of the apparatus.
This function can be obtained, for example, by means of a resistor connected between the substrate and the control region in which the substrate voltage is to be detected.
In power applications, the substrate can reach rather high voltage values (up to 2000 V) and the resistor connected therewith must be capable of withstanding the same voltage.
Particularly, when referring to resistive structures capable of detecting the voltage on an electrode (collector or drain) of a power component in monolith integrated semiconductor devices, the use of resistors destined to have high voltage applied to their terminals entails the need to make these resistors with a particularly high electrical resistance, for example higher than 100 KOhm.
Such high resistance values imply the use of considerably high resistance and/or long layers. Consequently, also when employing layers with the highest resistivity in technology, the integration of high voltage resistors implemented according to the prior art requires a large area of silicon.
For example, a serpentine resistive structure integrated on a semiconductor substrate is described in previous European Application EP-A-0996158.
A disadvantage of this type of structure is that the distances to be kept between one branch of the serpentine and another must be greater than the space-charge region which extends in the substrate. Since the substrate presents a low doping level, the dimension of this region is in the order of tens of microns when a high voltage difference is applied. An additional loss in terms of occupied area is produced in making annular regions or field plates of low concentration doped silicon surrounding the resistor to prevent premature breakdowns. Another problem related to this kind of resistor is the interaction with the on-board apparatus structures where they are inserted.
Another type of high voltage resistor of a known type employs a high resistivity semiconductor layer with conductivity opposite to that of the substrate surrounded by a layer of insulating material, for example silicon dioxide. This solution solves the problem of the space-charge region which would tend to short-circuit the facing branches of the resistor. This is because the depth of the insulating material regions is sufficient to prevent this event. However, this solution requires that the resistor be located near the high voltage region of the apparatus and only slightly reduces the occupied area. Furthermore, the possibility of interaction with the structures on-board the apparatus where the resistor is located still exists.
The embodiments of the invention are directed to a structure for a semiconductor resistive element and the respective manufacturing process.
In accordance with one embodiment, resistive structures capable, for example, of detecting the voltage present on an electrode (collector or drain) of the power component in monolith integrated semiconductor devices are provided.
The embodiments of the invention improve the previously known solutions in terms of electrical performance and manufacturing process. For this purpose, according to the currently preferred embodiment of the invention, a second epitaxial layer is grown on a first epitaxial layer and then a layer with a higher doping concentration than the second epitaxial layer, positioned over a buried region, is obtained by photolithography, ion implantation and diffusion. The buried region is of opposite conductivity type to the first epitaxial layer to define a resistive element. Ideally, the buried region includes subregions that are connected in marginal continuity relationship.